Lens in series to increase magnification

[Laerke]

Hello!
I am not an optical expert, so I will appreciate any advice on my topic. We have an imaging system which contains a lens, a camera and an object (film). The lens gives 2.3x magnification and its NA is around 0.09. Our system is monochrome - 405nm. We need to increase the magnification of the entire system by a factor of 2. The working distance from the lens to the object is quite large: 50 mm, which would allow inserting a magic glass, if such existed. But would it work in principle? After the magnification, I would like to imagine 2.7 micron features on film with a decent sharpness. i.e. MTF >0.5 at 190 lp/mm.
Searching around I came across Barlow lenses, but these to be inserted in front of the last optical element (if I understood it correctly), which is not an option, as I cannot modify the existing lens.What would be the way to go? Is there a chance that a single aspheric optical element solves this problem?

[MichaelG.]

Barlow lenses [a.k.a.tele-converters] are ‘negative’ and usually go after the complete lens, turning it into a telephoto. https://en.wikipedia.org/wiki/Barlow_lens
< but, see edit >

Close-up lenses are ‘positive’ and attach to the front of the lens, shortening its focal length.
https://en.wikipedia.org/wiki/Close-up_lens

Different solutions, but conceptually either would work ... with no need to modify the internals of your lens.

Both types are available at various quality levels; but I suspect you would struggle to meet your required resolution.

Can you provide any details of the lens that you are currently using ?

MichaelG.
.

Edit: I was thinking of the classic “35mm SLR” tele-converter ... but there are also front mounted devices which perform a similar function, and are popular for videocameras.
See here: http://www.ianperegian.com/My_FZ35_38_W ... rture.html

[apochronaut]

ditto on the information regarding your magnifier. you also did not provide any details regarding the distance from the lens to your camera?

[Laerke]

Can you provide any details of the lens that you are currently using ?

MichaelG.

Michael, thanks for the answer and the links - very useful.

We have a custom lens. Perhaps this image can give some clues about the setup:
The camera (Vieworks TDI 12k, M72) is on the left hand side and the gate where we put the film is to the right.

Working distance Lens to Object: 50 mm
Working distance Lens to Sensor: 31.7 mm
Entrance pupil object side: >2500
Exit pupil: >220
Object diameter or field of view: 26 mm (currently)

[Scarodactyl]

You might want to try asking over at the photomacrography.net forums as well. They probably have more collective experience with line scan optics in general.

[MichaelG.]

The camera (Vieworks TDI 12k, M72) is on the left hand side ...

.

I’m out of my depth already

Have just downloaded this, as ‘prep’
https://www.clearviewimaging.co.uk/hubf ... 6665080870

MichaelG.

[MichaelG.]

We have a custom lens. Perhaps this image can give some clues about the setup:

Intuitively ... that lens configuration appears to be ‘modular’
I suspect that the elements grouped near the camera are a ‘base-unit’ and the elements to the right are an optional telephoto group which can be selected to customise the lens.

Perhaps therefore, you could treat the [quite simple] telephoto group as what you need to modify ... ignoring the clever stuff near the camera.

MichaelG.
.

Edit: Just to keep us on the same page:
https://en.wikipedia.org/wiki/Telephoto ... hoto_1.svg
... shown [just to confuse] the other way round to your illustration

[Laerke]

You might want to try asking over at the photomacrography.net forums as well. They probably have more collective experience with line scan optics in general.

Will do, thanks for the direction.

[Laerke]

The camera (Vieworks TDI 12k, M72) is on the left hand side ...

.

I’m out of my depth already

Have just downloaded this, as ‘prep’
https://www.clearviewimaging.co.uk/hubf ... 6665080870

MichaelG.

Sure, this camera can do quite amazing things.

[Laerke]

We have a custom lens. Perhaps this image can give some clues about the setup:

Intuitively ... that lens configuration appears to be ‘modular’
I suspect that the elements grouped near the camera are a ‘base-unit’ and the elements to the right are an optional telephoto group which can be selected to customise the lens.

Perhaps therefore, you could treat the [quite simple] telephoto group as what you need to modify ... ignoring the clever stuff near the camera.

MichaelG.
.

Edit: Just to keep us on the same page:
https://en.wikipedia.org/wiki/Telephoto ... hoto_1.svg
... shown [just to confuse] the other way round to your illustration

I actually have the layout of this lens. You are probably right: the first group could be replaced. But looking at the physical lens... not sure how easy is to swap this module. Anyway, this would be a good alternative as well, something to investigate. Thanks for the idea.

[MichaelG.]

I actually have the layout of this lens. You are probably right: the first group could be replaced. But looking at the physical lens... not sure how easy is to swap this module. Anyway, this would be a good alternative as well, something to investigate. Thanks for the idea.

I was only ‘thinking aloud’ but ... what I had in mind was that if the assembly is modular, then an auxiliary “converter” of some sort might only need to be specified in relation to that first group [because the group near the camera must already be ‘versatile’]: It might therefore not degrade the performance so much as it would if the lens had been optimised as a piece.

Hope that makes some sort of sense ... I’m rambling !!

MichaelG.

[MichaelG.]

.

I am struggling to reconcile the two illustrations of your system

Does either of them represent the actual hardware, or are they both ‘typical’ arrangements ?

To make comparison easier, I mirrored your first image:
.

05B98F41-377E-4FD2-BB32-7825FC397F28.jpeg (86.31 KiB) Viewed 5602 times

.
But found it impossible to meaningfully overlay the dimensioned drawing ...

MichaelG.

[Laerke]

.

I am struggling to reconcile the two illustrations of your system

Does either of them represent the actual hardware, or are they both ‘typical’ arrangements ?

To make comparison easier, I mirrored your first image:
.
05B98F41-377E-4FD2-BB32-7825FC397F28.jpeg

.
But found it impossible to meaningfully overlay the dimensioned drawing ...

MichaelG.

Sorry for this. I just discovered that the rays tracing was for 16k camera. And the 3d drawing is the actual lens (12k) which we got from the supplier. The 16k sensor is 20 mm longer, but otherwise both lenses should be pretty similar.

[Laerke]

After more intensive digging, I managed to find the correct drawing:


I also found a confirmation in one of old emails that "this lens is double-telecentric".

[MichaelG.]

Excellent, thank you

I will have a look later ... to see if I can understand the basics of the design.

MichaelG.
.

Meanwhile ... here is the best tutorial I have seen about telecentric lenses:
https://schneiderkreuznach.com/applicat ... rement.pdf

and the subject of Double Telecentricity is covered briefly towards the end of this page:
https://www.edmundoptics.co.uk/knowledg ... gn-topics/
... EO also offers this video: https://youtu.be/O-NeZcmYyJ4

[blekenbleu]

We have an imaging system which contains a lens, a camera and an object (film).
The lens gives 2.3x magnification and its NA is around 0.09. Our system is monochrome - 405nm.
We need to increase the magnification of the entire system by a factor of 2.

You did not mention the camera type; some interchangeable lens systems (e.g. Canon, Nikon DSLR) have 2x telextender options.

[Laerke]

We have an imaging system which contains a lens, a camera and an object (film).
The lens gives 2.3x magnification and its NA is around 0.09. Our system is monochrome - 405nm.
We need to increase the magnification of the entire system by a factor of 2.

You did not mention the camera type; some interchangeable lens systems (e.g. Canon, Nikon DSLR) have 2x telextender options.

Camera VT-12K5X-H200, mount M72.

[MichaelG.]

After more intensive digging, I managed to find the correct drawing:


I also found a confirmation in one of old emails that "this lens is double-telecentric".

Hopefully, having followed my links, you will appreciate how that is illustrated in the drawing.
The central ray in each of the five bundles is parallel to the optical axis, on both the object side [input] and the image side [output] of the lens.

Doubling the magnification without losing telecentricity is probably near-impossible with an external attachment.

So the big question is ...
How important is double-telecentricity, when your object is a piece of film ?

MichaelG.

[Laerke]

Hopefully, having followed my links, you will appreciate how that is illustrated in the drawing.
The central ray in each of the five bundles is parallel to the optical axis, on both the object side [input] and the image side [output] of the lens.

Doubling the magnification without losing telecentricity is probably near-impossible with an external attachment.

So the big question is ...
How important is double-telecentricity, when your object is a piece of film ?

MichaelG.

I think the main advantage of telecentricity is in low geometric distortion, that's why this concept was chosen when designing our lens. But the distortions are not really a problem since we have tracking algorithms which fix it, unless the distortion is too strong. The most important is the MTF which should be at least 50% both at the centre and at the edges.

[MichaelG.]

The expedient first step might therefore be to put a high quality ‘close-up lens’ on the front of the system and see what results you get.

If you are using 405nm monochrome light then there should be no need for an achromat ... just get the best-figured lens you can find.

No guarantee that it will be in any way acceptable: But at least you would have a baseline for further investigation.

MichaelG.
.

Note: for ordinary photography ... I like the Minolta close-up lenses that were produced in the 1970s, but they might seriously degrade your sophisticated optics:
http://photojottings.com/wp-content/upl ... pchart.pdf
... should get you started though.

.

P.S. __ I’ve just re-read your comment:

I think the main advantage of telecentricity is in low geometric distortion, that's why this concept was chosen when designing our lens.

... and I think it may be worth me emphasising that the ‘low geometric distortion’ provided by telecentric lenses relates specifically to the imaging of three-dimensional objects. If your subject is a piece of film, then [at low magnifications] it is two-dimensional, and the telecentricity itself would seem redundant.

[Laerke]

The expedient first step might therefore be to put a high quality ‘close-up lens’ on the front of the system and see what results you get.

The first experiment I did was this: I put a microscope 4x NA=0.1 objective in front of my lens. It resulted in 1.5 magnification and the sharpness was nearly the same as I got in the microscope with the same objective. Which is definitely not I want, but at least it gave some hope that another close-up lens would work better. This also makes me set NA=0.25 as a goal, since an objective 10x 0.25 gives good results in Nikon microscope.

If you are using 405nm monochrome light then there should be no need for an achromat ... just get the best-figured lens you can find.

No guarantee that it will be in any way acceptable: But at least you would have a baseline for further investigation.

Sure, experiments is my most powerful tool at the moment.

Note: for ordinary photography ... I like the Minolta close-up lenses that were produced in the 1970s, but they might seriously degrade your sophisticated optics:
http://photojottings.com/wp-content/upl ... pchart.pdf
... should get you started though.

Good suggestion. Will try to get hold of some of these.

P.S. __ I’ve just re-read your comment:

I think the main advantage of telecentricity is in low geometric distortion, that's why this concept was chosen when designing our lens.

... and I think it may be worth me emphasising that the ‘low geometric distortion’ provided by telecentric lenses relates specifically to the imaging of three-dimensional objects. If your subject is a piece of film, then [at low magnifications] it is two-dimensional, and the telecentricity itself would seem redundant.

I agree with that.